The present invention relates to a power transmission device and a method of transmitting power, especially to a power transmission device and a method of transmitting power to a commercial electricity system.
When a direct current (DC) electric power is supplied to a commercial electricity system, the DC voltage is inverted to an alternating current (AC) voltage by an inverter, and then the inverted voltage is supplied to a commercial electricity system. The DC electric power is generated by a generator such as a solar battery and the like. The inverter modulates the voltage waveform by the pulse width modulation (PWM) to correct the error (difference) between the inverted AC waveform and the voltage waveform of a commercial electricity system.
For the PWM, a complex control circuit is required to control the frequency and phase of the voltage. This control circuit raises the price of the power transmission device as well as complicates the structure of the power transmission device.
And in the case where the inverter is damaged, there is a possibility of electric power generated by the generator leaking to a commercial electricity system without being controlled. Further, there is a possibility of devices connected to a commercial electricity system being damaged by an electricity leakage (i.e., a possibility of a secondary damage being caused).
The present invention was made in view of the above circumstances, and it is the first object of this invention to provide a power transmission device and a method of transmitting power which are simply composed.
Further, it is the second object of this invention to provide a power transmission device and a method of transmitting power which are low-cost.
And it is the third object of this invention to provide a power transmission device and a method of transmitting power which can prevent electricity from leaking from a generator to a commercial electricity system and consequently can prevent the occurrence of the secondary damage.
To achieve the above objects, the power transmitting device according to the first aspect of this invention is located between an AC (alternating current) power source (8) for generating an AC voltage and a DC (direct current) power source (2, 3, 4, and 5) for generating a DC voltage, and comprises:
a transfer switch (6) which is connected to between the DC power source and the AC power source and is for supplying the DC voltage to the AC power source or interrupting a supply of the DC voltage to the AC power source in accordance with a control signal provided thereto; and
an AC voltage monitor circuit (7) which is connected to the AC power source and the transfer switch and is for determining whether an absolute value of the AC voltage generated by the AC power source is equal to or higher than a predetermined threshold level or not, supplying the transfer switch with the control signal for controlling the transfer switch to supply the DC voltage to the AC power source in such a way as to provide the DC voltage with the same polarity as the AC voltage when determining that the absolute value is equal to or higher than the threshold level, and supplying the transfer switch with the control signal for controlling the transfer switch to interrupt the supply of the DC voltage to the AC power source when determining that the absolute value is lower than the threshold level.
According to this structure, the DC voltage output by the DC power source is supplied to the AC power source via the transfer switch or interrupted to be supplied depending on whether or not the AC voltage generated by the AC power source is higher than the voltage threshold level. Accordingly, there is no need for pulse-width modulation (PWM) and a complex control circuit necessary for PWM. Therefore, the structure will be simple.
An output impedance of the DC power source may be higher than that of the AC power source, and a voltage drop generated in an outside load which is connected to the AC power source by an electric current supplied from the DC power source may be higher than the AC voltage generated by the AC power source.
In this case, the voltage between both ends of the load is maintained approximately equal to the AC voltage generated by the AC power source.
The AC voltage monitor circuit may further comprise a half cycle monitor circuit (104) for determining whether or not a period of time in which the DC power source is supplying the DC voltage to the AC power source is over a half of a cycle of an AC electric power generated by the AC power source, and supplying the transfer switch with the control signal for controlling the transfer switch to interrupt the supply of the DC voltage from the DC power source to the AC power source when determining that the period of time is over the half of the cycle.
According to this half cycle monitor circuit, the AC power source is cut away from the DC power source when the AC power source is out of order so that a period of time in which the DC power source is supplying the DC voltage becomes over the half of the cycle of the AC voltage. Therefore, an electricity leakage from the DC power source to the AC power source can be prevented.
The transfer switch may comprise, for example:
a first switching element (T1) which comprises a first electric current path and a first control terminal;
a second switching element (T2) which comprises a second electric current path and a second control terminal;
a third switching element (T3) which comprises a third electric current path and a third control terminal; and
a fourth switching element (T4) which comprises a fourth electric current path and a fourth control terminal. In this case:
one end of the first electric current path and one end of the third electric current path may be connected to one of a pair of electrodes which are provided on the DC power source and are for outputting the DC voltage;
one end of the second electric current path and one end of the fourth electric current path may be connected to the other of the pair of electrodes provided on the DC power source;
the other end of the first electric current path and the other end of the fourth electric current path may be connected to one of a pair of electrodes which are provided on the AC power source and are for outputting the AC voltage; and
the other end of the second electric current path and the other end of the third electric current path may be connected to the other of the pair of electrodes provided on the AC power source.
And in this case, the AC voltage monitor circuit may:
determine whether a polarity of a voltage output from the one of the pair of electrodes provided on the DC power source is same as or different from that of a voltage output from the one of the pair of electrodes provided on the AC power source;
apply a voltage, for controlling the first and second electric current paths to turn on, to the first and second control terminals as the control signal, and apply a voltage, for controlling the third and fourth electric current paths to turn off (non-conductive), to the third and fourth control terminals as the control signal when determining that the absolute value of the AC voltage is equal to or higher than the threshold level, and that the polarity of the voltage output from the one of the pair of electrodes provided on the DC power source is same as that of the voltage output from the one of the pair of electrodes provided on the AC power source;
apply a voltage, for controlling the first and second electric current paths to turn off, to the first and second control terminals as the control signal, and apply a voltage for controlling the third and fourth electric current paths to turn on, to the third and fourth control terminals as the control signal when determining that the absolute value of the AC voltage is equal to or higher than the threshold level, and that the polarity of the voltage output from the one of the pair of electrodes provided on the DC power source is different from that of the voltage output from the one of the pair of electrodes provided on the AC power source; and
apply a voltage, for controlling the first to fourth electric current paths to turn off, to the first to fourth control terminals as the control signal when determining that the absolute value of the AC voltage is lower than the thresholde level.
The 1st switching element may be composed of, for example, a first field effect transistor (T1) whose drain and source serve as both ends of the first electric current path and whose gate serves as the first control terminal.
The second switching element may be composed of, for example, a second field effect transistor (T2) whose drain and source serve as both ends of the second electric current path and whose gate serves as the second control terminal.
The third switching element may be composed of, for example, a third field effect transistor (T3) whose drain and source serve as both ends of the third electric current path and whose gate serves as the third control terminal.
The fourth switching element may be composed of, for example, a fourth field effect transistor (T4) whose drain and source serve as both ends of the fourth electric current path and whose gate serves as the 4th control terminal.
The AC voltage monitor circuit may determine whether or not a period of time in which the DC power source is supplying the DC voltage to the AC power source is over a half of a cycle of an AC electric power generated by the AC power source, and may apply a voltage for controlling the first to fourth electric current passages to turn off, to the first to fourth control terminals as the control signal when determining that the period of time is over the half of the cycle.
According to this structure, the AC power source is cut away or isolated from the DC power source when the AC power source is out of order so that a period of time in which the DC power source is supplying the DC voltage becomes over the half of the cycle of the AC voltage. Therefore, an electricity leakage from the DC power source to the AC power source can be prevented.
The power transmission device according to the second aspect of this invention is located between an AC power source (8) for generating an AC voltage and a DC power source (2) for generating a first DC voltage, and comprises:
a DC-AC converter (3) for converting the first DC voltage into an AC voltage and outputting it;
an isolation transformer (4) for transforming the AC voltage output by the DC-AC converter and outputting it;
a rectifier (5) for rectifying the AC voltage output by the isolation transformer to generate a second DC voltage;
a transfer switch (6) which is connected to between the rectifier and the AC power source, and is for supplying the second DC voltage to the AC power source or interrupting a supply of the second DC voltage to the AC power source in accordance with a control signal supplied thereto; and
an AC voltage monitor circuit (7) which is connected to the AC power source and the transfer switch and is for determining whether an absolute value of the AC voltage generated by the AC power source is equal to or higher than a predetermined threshold level or not, supplying the transfer switch with the control signal for controlling the transfer switch to supply the second DC voltage to the AC power source in such a way as to provide the second DC voltage with the same polarity as the AC voltage when determining that the absolute value is equal to or higher than the threshold level, and supplying the transfer switch with the control signal for controlling the transfer switch to interrupt the supply of the second DC voltage to the AC power source when determining that the absolute value is lower than the threshold level.
According to this structure, the second DC voltage output by the rectifier is supplied to the AC power source via the transfer switch or interrupted to be supplied depending on whether or not the AC voltage generated by the AC power source is higher than the voltage threshold level. Accordingly, there is no need for pulse-width modulation (PWM) and a complex control circuit necessary for PWM. Therefore, the structure will be simple.
And according to this structure, the isolation transfer isolates the DC power source from the AC power source so that an electricity leakage between the DC power source and the AC power source is prevented.
An output impedance of the rectifier may be higher than that of the AC power source, and a voltage drop generated in an outside load which is connected to the AC power source by an electric current supplied from the rectifier may be higher than the AC voltage generated by the AC power source.
In this case, the voltage between both ends of the load is maintained approximately equal to the AC voltage generated by the AC power source.
The DC-AC converter may keep a level of the second DC voltage at an appropriate level by comprising:
an inverter (100) for inverting the first DC voltage into an AC voltage when the first DC voltage is applied thereto; and
a DC voltage monitor circuit (101) for determining whether a level of the first DC voltage has reached a set level or not, applying the first DC voltage to the inverter when determining that it has reached the set level, and preventing application of the first DC voltage to the inverter when determining that it has not reached the set level.
The method of transmitting power according to the third aspect of this invention is
a method of supplying a DC voltage to an AC power source which generates an AC voltage, wherein the method of transmitting power: determines whether an absolute value of the AC voltage generated by the AC power source is equal to or higher than a predetermined threshold level or not; supplies the DC voltage to the AC power source in such a way as to provide the DC voltage with the same polarity as the AC voltage when determining that the absolute value is equal to or higher than the threshold level; and interrupts a supply of the DC voltage to the AC power source when determining that the absolute value is lower than the threshold level.
According to this method, the DC voltage is supplied to the AC power source via a transfer switch or interrupted to be supplied depending on whether or not the AC voltage generated by the AC power source is higher than the voltage threshold level. Accordingly, there is no need for pulse-width modulation (PWM) and a complex control circuit necessary for PWM. Therefore, the structure for conducting this method will be simple.
An output impedance of a DC power source which generates the DC voltage may be higher than that of the AC power source, and a voltage drop generated in an outside load which is connected to the AC power source by an electric current supplied from the DC power source may be higher than the AC voltage generated by the AC power source.
In this case, the voltage between both ends of the load is maintained approximately equal to the AC voltage generated by the AC power source.
This method may determine whether or not a period of time in which the DC voltage is supplied to the AC power source is over a half of a cycle of an AC electric power generated by the AC power source, and may interrupt the supply of the DC voltage to the AC power source when determining that the period of time is over the half of the cycle.
According to this method, the AC power source is cut away from the power source of the DC voltage when the AC power source is out of order so that a period of time in which the power source of the DC voltage is supplying the DC voltage becomes over the half of the cycle of the AC voltage. Therefore, an electricity leakage from the power source of the DC voltage to the AC power source can be prevented.
In the case where the DC power source which generates the DC voltage comprises a pair of electrodes for outputting the DC voltage and the AC power source comprises a pair of electrodes for outputting the AC voltage, this method may:
whether a polarity of a voltage of one of the electrodes provided on the DC power source is same as or different from that of a voltage of one of the electrodes provided on the AC power source;
connect the one of the electrodes of the DC power source with the one of the electrodes of the AC power source, and connect the other of the electrodes of the DC power source with the other of the electrodes of the AC power source when determining that the absolute value of the AC voltage is equal to or higher than the threshold level, and that the polarity of the voltage of the one of the electrodes provided on the DC power source is same as the voltage of the one of the electrodes provided on the AC power source;
connect the one of the electrodes of the DC power source with the other of the electrodes of the AC power source, and connect the other of the electrodes of the DC power source with the one of the electrodes of the AC power source when determining that the absolute value of the AC voltage is equal to or higher than the threshold level, and that the polarity of the voltage of the one of the electrodes provided on the DC power source is different from that of the voltage of the one of the electrodes provided on the AC power source; and
cut between each of the electrodes provided on the DC power source and each of the electrodes provided on the AC power source when determining that the absolute value of the AC voltage is lower than the threshold level.
The DC voltage may be generated by converting a DC voltage for conversion into an AC voltage, transforming the AC voltage acquired from conversion by an isolation transformer, and rectifying the AC voltage acquired from transformation.
According to this method, the isolation transformer isolates a power source of the DC voltage for conversion from the AC power source so that an electricity leakage from the power source of the DC voltage for conversion to the AC power source can be prevented.
This method may determine whether a level of the DC voltage for conversion has reached a set level or not, and prevent the conversion of the DC voltage for conversion into an AC voltage when determining that the level of the DC voltage for conversion has reached the set level, so that the level of the DC voltage applied to the AC power source may be kept at an appropriate level.
The power transmission device according to the fourth aspect of this invention is a device for supplying a DC voltage generated by DC power sources (2, 3, 4, and 5) to an AC power source (8) for generating an AC voltage, and comprises:
determination means (7) for determining whether an absolute value of the AC voltage generated by the AC power source is equal to or higher than a predetermined threshold level or not;
means (6) for supplying the DC voltage to the AC power source in such a way as to provide the DC voltage with the same polarity as the AC voltage when the determination means determines that the absolute value of the AC voltage is equal to or higher than the threshold level; and
means (6) for interrupting a supply of the DC voltage to the AC power source when the determination means determines that the absolute value of the AC voltage is lower than the threshold level.
According to this structure, the DC voltage generated by the DC power sources is supplied to the AC power source or interrupted to be supplied depending on whether or not the AC voltage generated by the AC power source is higher than the voltage threshold level. Accordingly, there is no need for pulse-width modulation (PWM) and a complex control circuit necessary for PWM. Therefore, the structure will be simple.